RIPC-induced Cardioprotection Research Articles

Immediate Increase in the Root Mean Square of Successive Differences after Three Bouts of Remote Ischemic Preconditioning: A Randomized Controlled Trial.

(1) Background: Remote ischemic preconditioning (RIPC) is an intervention involving the application of brief episodes of ischemia and reperfusion to distant tissues to activate protective pathways in the heart. There is evidence suggesting the involvement of the autonomic nervous system (ANS) in RIPC-induced cardioprotection. This study aimed to investigate the immediate effects of RIPC on the ANS using a randomized controlled trial. (2) Methods: From March 2018 to November 2018, we conducted a single-blinded randomized controlled study involving 51 healthy volunteers (29 female, 24.9 [23.8, 26.4] years). Participants were placed in a supine position and heart rate variability was measured over 260 consecutive beats before they were randomized into either the intervention or the SHAM group. The intervention group underwent an RIPC protocol (3 cycles of 5 min of 200 mmHg ischemia followed by 5 min reperfusion) at the upper thigh. The SHAM group followed the same protocol but on the right upper arm, with just 40 mmHg of pressure inflation, resulting in no ischemic stimulus. Heart rate variability measures were reassessed afterward. (3) Results: The intervention group showed a significant increase in RMSSD, the possible marker of the parasympathetic nervous system (IG: 14.5 [5.4, 27.5] ms vs. CG: 7.0 [-4.3, 23.1 ms], p = 0.027), as well as a significant improvement in Alpha 1 levels compared to the control group (IG: -0.1 [-0.2, 0.1] vs. CG: 0.0 [-0.1, 0.2], p = 0.001). (4) Conclusions: Our results hint that RIPC increases the RMSSD and Alpha 1 parameters showing possible immediate parasympathetic modulations. RIPC could be favorable in promoting cardioprotective or/and cardiovascular effects by ameliorating ANS modulations.

Remote ischemic preconditioning-induced late cardioprotection: possible role of melatonin-mitoKATP-H2S signaling pathway.

Remote ischemic preconditioning (RIPC) confers cardioprotection against ischemia reperfusion (IR) injury. However, the precise mechanisms involved in RIPC-induced cardioprotection are not fully explored. The present study was aimed to identify the role of melatonin in RIPC-induced late cardioprotective effects in rats and to explore the role of H2S, TNF-α and mitoKATP in melatonin-mediated effects in RIPC. Wistar rats were subjected to RIPC in which hind limb was subjected to four alternate cycles of ischemia and reperfusion of 5 min duration by using a neonatal blood pressure cuff. After 24 h of RIPC or ramelteon-induced pharmacological preconditioning, hearts were isolated and subjected to IR injury on the Langendorff apparatus. RIPC and ramelteon preconditioning protected the hearts from IR injury and it was assessed by a decrease in LDH-1, cTnT and increase in left ventricular developed pressure (LVDP). RIPC increased the melatonin levels (in plasma), H2S (in heart) and decreased TNF-α levels. The effects of RIPC were abolished in the presence of melatonin receptor blocker (luzindole), ganglionic blocker (hexamethonium) and mitochondrial KATP blocker (5-hydroxydecanoic acid). RIPC produce delayed cardioprotection against IR injury through the activation of neuronal pathway, which may increase the plasma melatonin levels to activate the cardioprotective signaling pathway involving the opening of mitochondrial KATP channels, decrease in TNF-α production and increase in H2S levels. Ramelteon-induced pharmacological preconditioning may also activate the cardioprotective signaling pathway involving the opening of mitochondrial KATP channels, decrease in TNF-α production and increase in H2S levels.

Negative interaction between nitrates and remote ischemic preconditioning in patients undergoing cardiac surgery: the ERIC-GTN and ERICCA studies

Remote ischaemic preconditioning (RIPC) using transient limb ischaemia failed to improve clinical outcomes following cardiac surgery and the reasons for this remain unclear. In the ERIC-GTN study, we evaluated whether concomitant nitrate therapy abrogated RIPC cardioprotection. We also undertook a post-hoc analysis of the ERICCA study, to investigate a potential negative interaction between RIPC and nitrates on clinical outcomes following cardiac surgery. In ERIC-GTN, 185 patients undergoing cardiac surgery were randomized to: (1) Control (no RIPC or nitrates); (2) RIPC alone; (3); Nitrates alone; and (4) RIPC + Nitrates. An intravenous infusion of nitrates (glyceryl trinitrate 1 mg/mL solution) was commenced on arrival at the operating theatre at a rate of 2–5 mL/h to maintain a mean arterial pressure between 60 and 70 mmHg and was stopped when the patient was taken off cardiopulmonary bypass. The primary endpoint was peri-operative myocardial injury (PMI) quantified by a 48-h area-under-the-curve high-sensitivity Troponin-T (48 h-AUC-hs-cTnT). In ERICCA, we analysed data for 1502 patients undergoing cardiac surgery to investigate for a potential negative interaction between RIPC and nitrates on clinical outcomes at 12-months. In ERIC-GTN, RIPC alone reduced 48 h-AUC-hs-cTnT by 37.1%, when compared to control (ratio of AUC 0.629 [95% CI 0.413–0.957], p = 0.031), and this cardioprotective effect was abrogated in the presence of nitrates. Treatment with nitrates alone did not reduce 48 h-AUC-hs-cTnT, when compared to control. In ERICCA there was a negative interaction between nitrate use and RIPC for all-cause and cardiovascular mortality at 12-months, and for risk of peri-operative myocardial infarction. RIPC alone reduced the risk of peri-operative myocardial infarction, compared to control, but no significant effect of RIPC was demonstrated for the other outcomes. When RIPC and nitrates were used together they had an adverse impact in patients undergoing cardiac surgery with the presence of nitrates abrogating RIPC-induced cardioprotection and increasing the risk of mortality at 12-months post-cardiac surgery in patients receiving RIPC.

Increase of Cardioprotective Effectiveness of Remote Ischemic Preconditioning during Cardiac Surgery

The objective. To increase the effectiveness of cardioprotection during coronary artery bypass grafting (CABG) by using a modified technique of remote ischemic preconditioning (RIPC).Subjects and Methods. A prospective randomized study included 119 patients (aged 18 to 75 years) undergoing on-pump CABG. Patients were divided in 5 groups: Group 1 ‒ Sevoflurane control (ContrSevo), RIPC was not used, sevoflurane anesthesia (n = 24); Group 2 ‒ RIPC1 sevoflurane (RIP1Sevo), RIPC with ischemia-reperfusion of one lower limb, sevoflurane anesthesia (n = 26); Group 3 ‒ RIPC2 sevoflurane (RIP2Sevo), RIPC with ischemia-reperfusion of two lower limbs, anesthesia sevoflurane (n = 23); Group 4 ‒ Propofol control (ContrProp), RIPC was not used, propofol anesthesia (n = 22); Group 5 ‒ RIPC2 propofol (RIP2Prop), RIPC with ischemia-reperfusion of two lower limbs, propofol anesthesia (n = 24). The serum troponin I concentration (cTnI) (baseline, and 30 minutes, 12, 24, 36 and 48 hours after СPB weaning). Hemodynamic parameters and indicators of the clinical postoperative course also were evaluated. The impact ischemic-reperfused tissue mass of RIPC on the cardioprotection was assessed by comparing the groups of ContrSevo, RIPC1Sevo, and RIPC2Sevo. To assess the impact of propofol on the RIPC-induced cardioprotection, the groups of ContrProp and RIPC2Prop were compared.Results. Statistically significant differences in cTnI were found between the ContrSevo and the RIPC2Sevo at points of 12, 24 and 36 hours: ContrSevo 1.83 (1.3; 2.24) ng/ml, RIP2Sevo 1.28 (0.75; 1.63) ng/ml after 12 hours (p = 0.02), ContrSevo 1.44 (0.98; 2.26) ng/ml, RIPC2Sevo 1.17 (0.55; 1.66) ng/ml after 24 hours (p = 0.046), ContrSevo 1.26 (0.86; 1.72) ng/ml, and RIPC2Sevo 0.81 (0.47; 1.24) ng/ml after 36 hours (p = 0.035). No differences in the cTnI were found between the groups of ContrSevo and RIPC1Sevo, RIPC1Sevo and RIPC2Sevo at any stage of the study. There were no statistically significant differences between the groups when comparing hemodynamic parameters. In the RIPC2Sevo Group, arrhythmias requiring cardioversion or drug therapy were significantly less frequent compared to ContrSevo (1 vs. 6) (p = 0.047). There were no other significant differences in the postoperative clinical course. When comparing the groups of ContrProp and RIP2Prop, no significant differences were found in cTnI and hemodynamic parameters as well as in the postoperative clinical course.Conclusions. A greater mass of ischemic-reperfused peripheral tissue is accompanied by greater RIPC-induced cardioprotection. A modified protocol for RIPC with ischemia-reperfusion of two lower limbs with sevoflurane anesthesia enhances cardioprotection during on-pump CABG. The modified RIPC protocol with ischemia-reperfusion of two lower limbs with sevoflurane anesthesia reduces the risk of arrhythmias requiring cardioversion or drug therapy. Propofol inhibits the RIPC-induced cardioprotection with ischemia-reperfusion of two lower limbs.

Remote Ischemic Preconditioning induces Cardioprotective Autophagy and Signals through the IL-6-Dependent JAK-STAT Pathway.

Autophagy is a cellular process by which mammalian cells degrade and assist in recycling damaged organelles and proteins. This study aimed to ascertain the role of autophagy in remote ischemic preconditioning (RIPC)-induced cardioprotection. Sprague Dawley rats were subjected to RIPC at the hindlimb followed by a 30-min transient blockade of the left coronary artery to simulate ischemia reperfusion (I/R) injury. Hindlimb muscle and the heart were excised 24 h post reperfusion. RIPC prior to I/R upregulated autophagy in the rat heart at 24 h post reperfusion. In vitro, autophagy inhibition or stimulation prior to RIPC, respectively, either ameliorated or stimulated the cardioprotective effect, measured as improved cell viability to mimic the preconditioning effect. Recombinant interleukin-6 (IL-6) treatment prior to I/R increased in vitro autophagy in a dose-dependent manner, activating the Janus kinase/signal transducers and activators of transcription (JAK-STAT) pathway without affecting the other kinase pathways, such as p38 mitogen-activated protein kinases (MAPK), and glycogen synthase kinase 3 Beta (GSK-3β) pathways. Prior to I/R, in vitro inhibition of the JAK-STAT pathway reduced autophagy upregulation despite recombinant IL-6 pre-treatment. Autophagy is an essential component of RIPC-induced cardioprotection that may upregulate autophagy through an IL-6/JAK-STAT-dependent mechanism, thus identifying a potentially new therapeutic option for the treatment of ischemic heart disease.

The timing of propofol administration affects the effectiveness of remote ischemic preconditioning induced cardioprotection in rats.

The cardioprotection of remote ischemic preconditioning (RIPC) is abolished under propofol maintained anesthesia. Transient receptor potential vanilloid 1 (TRPV1) channel is present in the heart, and its activation could induce cardioprotection. Therefore, we tested whether the anesthetic propofol administration phase interfered with the RIPC-induced cardioprotection, and RIPC-induced cardioprotection via the cardiac TRPV1 channel. Male Sprague-Dawley rats were subjected to myocardial 30 minutes of ischemia followed by 2 hours of reperfusion. RIPC consisted of three cycles of 5-minute ischemia/reperfusion applied to a hindlimb. Propofol infusion at 12 mg/kg/h was commenced either at 10 minutes before the start of RIPC in the P-pre + RIPC group, or immediately after myocardial ischemia at the onset of reperfusion (P-post + RIPC) while performing RIPC. These two propofol infusion regimes were applied to another two grou bs without RIPC (P-pre and P-post groups). Infarct size (IS) was assessed by triphenyltetrazolium staining. Heart TRPV1 expression was detected by Western blot and immunofluorescence. RIPC significantly reduced myocardial IS compared with the control group (36.7 ± 3% versus 57.2 ± 4%; P < .01). When propofol was started before RIPC, the IS sparing effect of RIPC was completely abolished. However, propofol infusion starting immediately after myocardial ischemia did not affect RIPC-induced cardioprotection. TRPV1 expression significant increase after RIPC, then propofol inhibited the TRPV1 activation of RIPC if given before RIPC but not after. Our results suggest that the timing of propofol administration is critical to preserve the cardioprotection of RIPC. Propofol might cancel RIPC-induced cardioprotection via the cardiac TRPV1 receptor.

Investigating the role of acute and repeated stress on remote ischemic preconditioning-induced cardioprotection.

Objective(s):To study the effect of acute and repeated stress on cardioprotection-induced by remote ischemic preconditioning (RIPC).Materials and Methods:RIPC was induced by giving 4 short cycles of ischemia and reperfusion, each consisting of five min. The Langendorff’s apparatus was used to perfuse the isolated rat hearts by subjecting the hearts to global ischemia of 30 min and reperfusion of 120 min. The coronary effluent was collected to measure the levels of lactate dehydrogenase (LDH) and creatine kinase (CK) for the assessment of injury to the myocardium. Myocardial infarct size was measured by the use of triphenyl tetrazolium chloride. Acute stress was induced by subjecting the animals to cold immersion stress for 5 min. However, in the case of stress adaptation, rats were exposed to a homotypic stressor (cold-water immersion stress) each of 5 min duration for five consecutive days. Results:RIPC demonstrated a significant decrease in ischemia-reperfusion-induced myocardial injury in terms of decrease in LDH, CK, and infarct size. However, acute stress for five minutes prior to RIPC significantly abolished its cardioprotective effects. Exogenous administration of adenosine restored RIPC-induced cardioprotective effects in the presence of acute stress. On repeated stress exposure for 5 days, stress adaptation was noted, and there was no effect of repeated stress exposure on RIPC-induced cardioprotection. However, the cardioprotective effects of adenosine were absent in the case of rats subjected to repeated episodes of stress.Conclusion:Acute stress, but not repeated stress exposure, may alter the release of adenosine during RIPC, which may be manifested in the form of reduced cardioprotection during ischemic-reperfusion injury.

Pharmacological Inhibition of PTEN Restores Remote Ischemic Postconditioning Cardioprotection in Hypercholesterolemic Mice: Potential Role of PTEN/AKT/GSK3β SIGNALS.

Although remote ischemic postconditioning (RIPC) was shown to confer cardioprotection against myocardial ischemia/reperfusion (I/R) injury in normal animals, whether RIPC-induced cardioprotection is altered in the presence of hypercholesterolemia, a comorbidity with acute myocardial infarction (AMI) patients has yet to be determined. Normal or 2% cholesterol chow was fed to male C57BL/6J mice for 12 weeks to induce hypercholesterolemia, then normal or hypercholesterolemic murine hearts were exposed to AMI by coronary artery ligation. RIPC was induced by four episodes of 5 min femoral artery occlusion followed by 5 min reperfusion immediately after myocardial reperfusion in mice. Following I/R, RIPC significantly attenuated postischemic infarct size, hindered cardiomyocyte apoptosis, improved cardiac systolic function, decreased phosphatase and tensin homolog deleted on chromosome ten (PTEN) expression, and further increased Akt and GSK-3β phosphorylation in non-hypercholesterolemic, but not in hypercholesterolemic mice. Application of the PTEN inhibitor bisperoxovanadium (BpV) (1.0 mg/kg) reduced postischemic infarct size, attenuated cardiomyocyte apoptosis, and improved cardiac dysfunction in normal, but not in hypercholesterolemic mice. Further, increased dose of BpV (2 mg/kg or 10 mg/kg) failed to rescue the detrimental effects of hypercholesterolemia on I/R in mice following I/R. Especially important, we demonstrated that the combination BpV and RIPC exerted marked cardioprotective effects both in normal and hypercholesterolemic mice with I/R, indicating that PTEN inhibition restores RIPC-elicited myocardial protection in the presence of hypercholesterolemia. Our results demonstrated that hypercholesterolemia attenuated RIPC-induced cardioprotection against I/R injury by alteration of PTEN/Akt/GSK3β signals, and inhibition of PTEN rescued RIPC-induced cardioprotection in the presence of hypercholesterolemia.

Exploring the role and inter-relationship among nitric oxide, opioids, and KATP channels in the signaling pathway underlying remote ischemic preconditioning induced cardioprotection in rats.

Objective(s):This study explored the inter-relationship among nitric oxide, opioids, and KATP channels in the signaling pathway underlying remote ischemic preconditioning (RIPC) conferred cardioprotection. Materials and Methods:Blood pressure cuff was placed around the hind limb of the animal and RIPC was performed by 4 cycles of inflation (5 min) followed by deflation (5 min). An ex vivo Langendorff’s isolated rat heart model was used to induce ischemia (of 30 min duration)-reperfusion (of 120 min duration) injury. Results:RIPC significantly decreased ischemia-reperfusion associated injury assessed by decrease in myocardial infarct, LDH and CK release, improvement in postischemic left ventricular function, LVDP, dp/dtmax, and dp/dtmin. Pretreatment with L-NAME and naloxone abolished RIPC-induced cardioprotection. Moreover, preconditioning with sodium nitroprusside (SNP) and morphine produced a cardioprotective effect in a similar manner to RIPC. L-NAME, but not naloxone, attenuated RIPC and SNP preconditioning-induced increase in serum nitrite levels. Morphine preconditioning did not increase the NO levels, probably suggesting that opioids may be the downstream mediators of NO. Furthermore, glibenclamide and naloxone blocked cardioprotection conferred by morphine and SNP, respectively. Conclusion: It may be proposed that the actions of NO, opioids, and KATP channels are interlinked. It is possible to suggest that RIPC may induce the release of NO from endothelium, which may trigger the synthesis of endogenous opioids, which in turn may activate heart localized KATP channels to induce cardioprotection.

Stat5-dependent cardioprotection in late remote ischaemia preconditioning.

To study the protective effects of late remote ischaemic preconditioning (RIPC) against myocardial ischaemia/reperfusion (I/R) injury and determine whether Stat5 is involved in this protection by using cardiomyocyte-specific Stat5 knockout mice (Stat5-cKO). Mice were exposed to lower limb RIPC or sham ischaemia. After 24 h, the left anterior descending artery (LAD) was ligated for 30 min, then reperfused for 180 min. The myocardial infarct size (IS), apoptotic rate of cardiomyocytes, and serum myocardial enzymes were measured to evaluate for cardioprotective effects. Heart tissues were harvested to determine the cardiomyocytes' anti-apoptotic and survival signaling. When compared with the Stat5fl/fl mice without RIPC, Stat5fl/fl mice with RIPC (Stat5fl/fl+RIPC + I/R) displayed a decreased myocardial IS/LV (16 ± 1.5 vs. 30.1 ± 3.1%, P < 0.01; IS/ area at risk (AAR), 42.2 ± 3.5 vs. 69.2 ± 4.9%, P < 0.01), a reduced cardiomyocyte apoptotic rate (2.1 ± 0.37 vs. 5.5 ± 0.53%, P < 0.01), and lower creatine kinase (CK), lactate dehydrogenase (LDH), and creatine kinase-MB (CK-MB) levels. To the contrary, the Stat5-cKO mice (Stat5fl/fl; Tnnt2Cremice with Doxycycline treatment for 7 days) did not exhibit any effect of RIPC-induced cardioprotection. Activation of STAT5 protein was significantly higher in the Stat5fl/fl+RIPC + I/R group than in the Stat5fl/fl+I/R group, while there was no significant difference between the Stat5-cKO + RIPC + I/R and the Stat5-cKO + I/R group. Further analyses with heart tissues detected decreased protein expressions of cytochrome c (Cyt c) and cleaved Caspase-3 in the Stat5fl/fl+RIPC + I/R mice, along with increased anti-apoptotic molecules, including B-cell lymphoma-extra large (Bcl-xL) and B-cell lymphoma-2 (Bcl-2); such changes were not noted in the Stat5-cKO + RIPC + I/R mice. Additionally, RIPC increased cardiac hypoxia inducible factor-1 (HIF-1α) and interleukin-10 (IL10) protein levels and caused activation of AKT, phosphatidylinositol 3 kinase (PI3K), and vascular endothelial growth factor in the heart of the Stat5fl/fl mice. However, these changes were completely inhibited by the absence of Stat5. These results suggest that RIPC-induced late cardioprotection against myocardial I/R injury is Stat5-dependent and is correlated with the activation of anti-apoptotic signaling and cardiomyocyte-survival signaling.

Hypercholesterolemia Abrogates Remote Ischemic Preconditioning-Induced Cardioprotection: Role of Reperfusion Injury Salvage Kinase Signals.

Remote ischemic preconditioning (RIPC) is one of the most powerful intrinsic cardioprotective strategies discovered so far and experimental data indicate that comorbidity may interfere with the protection by RIPC. Therefore, we investigate whether RIPC-induced cardioprotection was intact in hypercholesterolemic rat hearts exposed to ischemia reperfusion in vivo. Normal or hypercholesterolemic rat hearts were exposed to 30 min of ischemia and 2 h of reperfusion, with or without RIPC, PI3K inhibitor wortmannin, MEK-ERK1/2 inhibitor PD98059, GSK3β inhibitor SB216763. Infarct size, apoptosis, MG53, PI3K-p85, p-Akt, p-ERK1/2, p-GSK3β, and cleaved Caspase-3 were determined. RIPC reduced infarct size, limited cardiomyocyte apoptosis following IR that was blocked by wortmannin but not PD98059. RIPC triggered unique cardioprotective signaling including MG53, phosphorylation of Akt, and glycogen synthase kinase-3ß (GSK3β) in concert with reduced proapoptotic active caspase-3. In contrast, RIPC failed to reduce myocardial necrosis and apoptosis as well as to increase the phosphorylated Akt and GSK3β in hypercholestorolemic myocardium. Importantly, we found that inhibition of GSK with SB216763 reduced myocardial infarct size in healthy and hypercholesterolemic hearts, but no additional cardioprotective effect was achieved when combined with RIPC. Our results suggest that acute GSK3β inhibition may provide a novel therapeutic strategy for hypercholesterolemic patients during acute myocardial infarction, whereas RIPC is less effective due to signaling events that adversely affect GSK3β.

Role of ATP-Sensitive Potassium Channels in Remote Ischemic Preconditioning Induced Tissue Protection.

Remote ischemic preconditioning (RIPC) is an innovative treatment strategy that alleviates ischemia-reperfusion injury, whereby short episodes of regional ischemia and reperfusion delivered to remote organs including hind limb, kidney and intestine, and so on provide protection to the heart. The RIPC is known to reduce infarct size, serum levels of cardiac enzymes, and myocardial dysfunction in various animal species as well as in patients. There have been a large number of studies suggesting that the ATP-sensitive potassium channels (KATP channel) play a significant role as a mediator or end effector in RIPC. The present review discusses the role of KATP channels and possible mechanisms in RIPC-induced cardioprotection.

Opioids in Remote Ischemic Preconditioning-Induced Cardioprotection.

Remote ischemic preconditioning (RIPC) is an intriguing process whereby transient regional ischemia and reperfusion episodes to remote tissues including skeletal, renal, mesenteric provide protection to the heart against sustained ischemia-reperfusion-induced injury. Clinically, this technique has been used in patients undergoing various surgical interventions including coronary artery bypass graft surgery, abdominal aortic aneurysm repair, percutaneous coronary intervention, and heart valve surgery. The endogenous opioid system is extensively expressed in the brain to modulate pain sensation. Besides the role of opioids in relieving pain, numerous researchers have found their critical involvement in evoking cardioprotective effects. Endogenous opioids including endorphins, enkephalins, and dynorphins are released during RIPC and are critically involved in mediating RIPC-induced cardioprotective effects. It has been suggested that during RIPC, the endogenous opioids may be released into the systemic circulation and may travel via bloodstream that act on the myocardial opioid receptors to induce cardioprotection. The present review describes the potential role of opioids in mediating RIPC-induced cardioprotection.

Investigations on the role of leukotrienes in remote hind limb preconditioning-induced cardioprotection in rats

The cardioprotective effects of remote hind limb preconditioning (RIPC) are well established, but its mechanisms still remain to be explored. Therefore, the present study was aimed to explore the possible involvement of 5-lipoxygenase-derived leukotrienes in RIPC. The hind limb was tied by a pressure cuff and was subjected to four episodes of inflation and deflation (5min each) to induce remote hind-limb preconditioning. Thereafter, the hearts were isolated and were subjected to global ischemia (30min) followed by reperfusion (120min) on the Langendorff apparatus. The extent of myocardial injury was assessed by measuring lactate dehydrogenase (LDH) and creatine kinase (CK) levels in the coronary effluent; the infarct size using TTC staining, and the hemodynamic parameters including LVDP, dp/dtmax and dp/dtmin. RIPC significantly decreased ischemia and reperfusion-induced increase in LDH, CK release, infarct size and improved LVDP, dp/dtmax and dp/dtmin. Administration of montelukast, leukotriene receptor antagonist (10 and 20mg/kg) and zileuton, 5-lipoxygenase inhibitor, (2.5 and 5mg/kg) abolished RIPC-induced cardioprotection. It may be concluded that hind limb ischemia stimulates 5-lipoxygenase to release leukotrienes which may elicit cardioprotection by humoral or neurogenic pathway.

0059 : The involvement of a cocktail of amino acids in remote ischemic preconditioning induced cardioprotection in acute myocardial infarction

Remote ischemic preconditionning (RIPC) has emerged as an attractive therapeutic procedure to protect the heart against ischemia/reperfusion (I/R) injury. Despite strong evidences of the critical role played by circulating humoral mediators for signal transduction, their identities still remain unknown. Using a targeted metabolomic approach we previously identified Glycine (GLY) and Kynurenine (KYN) as potential mediators for RIPC induced cardioprotection in both rats and humans. this study sought to determine whether a treatment with GLY and KYN alone or in combination could mimic the cardioprotective effect of the RIPC. Wistar rats, 8-10 weeks exposed to myocardial I/R were allocated to one of the following six groups: Myocardial Infarction (MI) , rats were subjected to myocardial I/R without any further intervention; RIPC+MI , four cycles of limb I/R were applied prior to the myocardial ischemia; Metabolites+ MI , with intraperitoneal (ip) injection of a combined GLY (0.5mg/g body weight) and KYN (0.3 mg/g body weight) 10 min before MI; Vehicle+MI , with ip injection of the vehicle 10 min before MI; GLY+MI , with ip injection of single dose of GLY 10 min before MI; and KYN+MI , with an ip injection of single dose of KYN 10 min prior to MI. Hearts were excised after 2h of reperfusion, the area at risk (AAR) and infarct size (AN) were measured after TTC staining. GLY and KYN plasma concentrations were determined by mass spectroscopy LC-MS/MS at 3 points of time: 15, 30 and 45 min after the ip injection. The metabolites blood assay showed a significant increase of both glycine and kynurenine in blood plasma 15 min after the intraperitoneal injection with a peak at 30 min. As compared to MI , both RIPC+MI and Metabolites+MI exhibited a smaller infarct size (AN/AAR=39.59±3.76% for Vehicle+MI vs. 27.15±4.47% for the Metabolites+MI group, and 42.49±2.42% for MI vs. 34.53±2.28% for the RIPC+MI , both p <0.05). Kynurenine injection alone and Glycine injection alone significantly decreased infarct size (AN/AAR=27.70±2.53% in Kynurenine+MI vs. MI group; p =0.0018 and 33.24±2.30% in Glycine+MI , vs. MI, p=0.006 ). We report that RIPC-induced cardioprotection may involve a cocktail of amino acids for signal transduction from the remote organ to the myocardium. The author hereby declares no conflict of interest

REMOTE ISCHEMIC CONDITIONING INFLUENCES MITOCHONDRIAL DYNAMICS.

Remote ischemic preconditioning (RIPC) has emerged as an attractive strategy to protect the heart against ischemia-reperfusion (I/R) injury. The mechanisms by which remote ischemic conditioning (RIC) is protective are to date unknown, yet a well-accepted theory holds that the mitochondria play a central role. Mitochondria are dynamic organelles that undergo fusion and fission. Interventions that decrease mitochondrial fission or increase mitochondrial fusion have been associated with reduced I/R injury. However, whether RIPC influences mitochondrial dynamics or not has yet to be ascertained.We sought to determine the role played by mitochondrial dynamics in RIPC-induced cardioprotection. Male adult rats exposed in vivo to myocardial I/R were assigned to one of two groups, either undergoing 40 min of myocardial ischemia followed by 120 min of reperfusion (MI group) or four 5-min cycles of limb ischemia interspersed by 5 min of limb reperfusion, immediately prior to myocardial ischemia and 120 min of reperfusion (MI+RIPC group). After reperfusion, infarct size was assessed and myocardial tissue was analyzed by Western blot and electron microscopy. RIPC induced smaller infarct size (-28%), increased mitochondrial fusion protein OPA1, and preserved mitochondrial morphology. These findings suggest that mitochondrial dynamics play a role in the mechanisms of RIPC-induced cardioprotection.

Possible role of thromboxane A2 in remote hind limb preconditioning-induced cardioprotection.

Remote hind limb preconditioning (RIPC) is a protective strategy in which short episodes of ischemia and reperfusion in a remote organ (hind limb) protects the target organ (heart) against sustained ischemic reperfusion injury. The present study was designed to investigate the possible role of thromboxane A2 in RIPC-induced cardioprotection in rats. Remote hind limb preconditioning was performed by four episodes of 5 min of inflation and 5 min of deflation of pressure cuff. Occlusion of the hind limb with blood pressure cuff is most feasible, non-invasive, clinically relevant, and safe method for inducing RIPC. Isolated rat hearts were perfused on Langendorff apparatus and were subjected to global ischemia for 30 min followed by 120-min reperfusion. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) were measured in coronary effluent to assess the degree of myocardial injury. The extent of myocardial infarct size along with the functional parameters including left ventricular developed pressure (LVDP), dp/dtmax, and dp/dtmin were also measured. Ozagrel (thromboxane synthase inhibitor) and seratrodast (thromboxane A2 receptor antagonist) were employed as pharmacological modulators of thromboxane A2. Remote hind limb preconditioning significantly attenuated ischemia/reperfusion-induced myocardial injury and produced cardioprotective effects. However, administration of ozagrel and seratrodast completely abolished the cardioprotective effects of RIPC suggesting the key role of thromboxane A2 in RIPC-induced cardioprotection. It may be concluded that brief episodes of preconditioning ischemia and reperfusion activates the thromboxane synthase enzyme that produces thromboxane A2, which may elicit cardioprotection either involving humoral or neurogenic pathway.

RISK and SAFE signaling pathway involvement in apolipoprotein A-I-induced cardioprotection.

Recent findings indicate that apolipoprotein A-I (ApoA-I) may be a protective humoral mediator involved in remote ischemic preconditioning (RIPC). This study sought to determine if ApoA-I mediates its protective effects via the RISK and SAFE signaling pathways implicated in RIPC. Wistar rats were allocated to one of the following groups. Control: rats were subjected to myocardial ischemia/reperfusion (I/R) without any further intervention; RIPC: four cycles of limb I/R were applied prior to myocardial ischemia; ApoA-I: 10 mg/Kg of ApoA-I were intravenously injected prior to myocardial ischemia; ApoA-I + inhibitor: pharmacological inhibitors of RISK/SAFE pro-survival kinase (Akt, ERK1/2 and STAT-3) were administered prior to ApoA-I injection. Infarct size was significantly reduced in the RIPC group compared to Control. Similarly, ApoA-I injection efficiently protected the heart, recapitulating RIPC-induced cardioprotection. The ApoA-I protective effect was associated with Akt and GSK-3β phosphorylation and substantially inhibited by pretreatment with Akt and ERK1/2 inhibitors. Pretreatment with ApoA-I in a rat model of I/R recapitulates RIPC-induced cardioprotection and shares some similar molecular mechanisms with those of RIPC-involved protection of the heart.

Effects of remote ischemic preconditioning and myocardial ischemia on microRNA-1 expression in the rat heart in vivo.

Remote ischemic preconditioning (RIPC) is an easily applicable method for protecting the heart against a subsequent ischemia and reperfusion (I/R) injury. However, the exact molecular mechanisms underlying RIPC are unknown. We examined the involvement of microRNAs (miRNAs) and in particular the expression of miRNA-1 (miR-1) in RIPC and myocardial ischemia. Remote ischemic preconditioning was conducted by four cycles of 5-min bilateral hind-limb ischemia in male Wistar rats. Cardiac ischemia was induced by ligation of the left anterior descending coronary artery for 35 min followed by 2 or 6 h of reperfusion. MicroRNA expression was analyzed by Taqman miRNA arrays and quantitative polymerase chain reaction assays. Luciferase assays were performed to validate the miR-1 target gene brain-derived neurotrophic factor (BDNF). Brain-derived neurotrophic factor mRNA and protein levels were analyzed by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Remote ischemic preconditioning led to a differential expression of miRNAs. The most abundant cardiac miRNA, miR-1, was downregulated by RIPC without following ischemia as well as after I/R and RIPC followed by I/R after 2 h of reperfusion. After 6 h of reperfusion, RIPC led to an upregulation of miR-1, whereas ischemia had no effect on miR-1 expression. Luciferase assays confirmed the interaction of miR-1 with BDNF, a protein that has been shown to exert cardioprotective effects. Brain-derived neurotrophic factor protein levels in rat hearts measured by enzyme-linked immunosorbent assay were not significantly altered after 2 or 6 h of reperfusion in all intervention groups. Remote ischemic preconditioning leads to changes in the expression levels of the most abundant cardiac miRNA, miR-1. MicroRNA 1 levels did not correlate with protein levels of BDNF, a known miR-1 target, in vivo. Further studies are needed to explore the biological significance of changes in miR-1 expression levels and the potential interaction with BDNF in RIPC-induced cardioprotection.

Clinical Benefits of Remote Ischemic Preconditioning

In the 2 decades since the first report of the infarct-sparing effect of remote ischemic preconditioning (RIPC), the concept has evolved from a provocative laboratory observation to the focus of multiple phase II clinical trials.1–4 Investigation of RIPC in patient populations has largely centered on the assessment of surrogate biomarkers of cardiac injury (ie, cardiac troponins and creatine kinase) after cardiac surgery, with emerging evidence of improvement in long-term clinical outcome.3–5 Moreover, with rare exceptions, previous clinical trials have not been designed to yield insight into the cellular mechanisms underlying the protection afforded by RIPC. Accordingly, the recent publication by Slagsvold et al6 provides multiple, novel contributions to our understanding of RIPC-induced cardioprotection: focusing on atrial myocardium, the authors report preservation of mitochondrial respiration and modified expression of microRNAs, together with an attenuation in the incidence of postoperative atrial fibrillation in patients randomized to receive RIPC before coronary artery bypass graft surgery.6 Article, see p 851 The hallmark of myocardial ischemia–reperfusion injury associated with coronary artery bypass graft surgery is the well-described increase in plasma concentration of cardiac enzymes during the initial 48 to 72 hours after release of the aortic clamp. Plasma levels of troponins or creatine kinase are not, however, the sole markers of cardiac damage. A substantial proportion of patients reportedly develop atrial fibrillation during the first 3 postoperative days, a complication associated with long-term adverse outcomes including increased mortality.7,8 Indeed, in 2010, a phase II multicenter trial was initiated to test the hypothesis that RIPC would reduce the incidence of atrial fibrillation after coronary artery bypass graft surgery.8 Slagsvold et al,6 in their single-center study, found that 14% versus 50% of patients in the RIPC versus control groups developed atrial fibrillation during the …